Musical instrument performance amplifiers such as, for example, the amplifier employed with an electric guitar, are quite different in a number of respects from those amplifiers, such as the amplifier of a high fidelity music system, wherein previously generated sound or music is to be precisely reproduced. In the high fidelity system desirable amplifier characteristics include a flat response. Performance of such an amplifier may be measured in part by the flatness of the response over a wide range of musical input frequencies and, in addition, freedom from ringing or sustaining of tones (damping) and minimum generation of overtones or harmonics.
In the musical instrument performance amplifier, on the other hand, the very characteristics that improve the high fidelity music reproducing amplifier are undesirable and would cause the sound of the instrument played through such an amplifier to sound flat, dull and uninteresting to the ears of a great majority of listeners.
Tube type amplifiers for use with a performing instrument such as a guitar, for example, have frequently included a pair of pentodes connected in push-pull to an output transformer and have required some feedback for various reasons including hum reduction.
Since the advent of transistors, increasingly greater numbers of amplifiers have been made with transistors instead of tubes. At present, a large majority of high fidelity sound reproducing amplifiers have transistor output sections. Commonly, transistor amplifiers, whether of the sound reproducing type or of the musical instrument performance type, employ bipolar output transistors which have a low output impedance. The low output impedance of such bipolar amplifiers helps to provide the flat highly damped response that is so desirable in the high fidelity reproducing system. This response is even further enhanced by the required provision of large amounts of feedback.
Tube type amplifiers provide higher source impedance to a speaker and provide musical instrument sound via the speaker that is more pleasant to the listener. The tube amplifier may provide some sustain of sounds reproduced by the speaker, but not the greater sustain that is most frequently desired. Further, its reproduction of harmonics, is at a decreased power, decreasing as frequency increases. The transistor amplifier, when used in applications for a musical instrument performance type amplifier, exhibits the many advantages of the transistor, including small size, lower power requirements, less heat generation and faster response time. Nevertheless, it finds little popularity in such application because of its lack of sustain and attenuated harmonics.
Accordingly, it is an object of the present invention to provide a performance amplifier for an electrical musical instrument which exhibits advantages of the transistor and yet provides significantly improved performance of the type desired in the creation of music by the playing of an electrical musical instrument.